Embodiments of the disclosure relate to ultrasound imaging, and more particularly to acoustic radiation force imaging with enhanced performance.
Ultrasonography is an ultrasound-based diagnostic medical imaging technique used to visualize muscles, tendons, and many internal organs to capture their size, structure and any pathological lesions using near real-time tomographic images. Ultrasonography also finds use in therapeutic procedures where ultrasound is used to guide interventional procedures, such as biopsies or drainage of fluid collections. Conventionally, an ultrasonographic system operates by applying acoustic energy with a frequency, for example, in the range of 1-18 Mhz, although higher frequencies have been used in certain applications.
A typical ultrasonographic system employs a probe including one or more acoustic transducers such as piezoelectric transducers for delivering brief ultrasound pulses to a target region. Accordingly, the probe may be coupled to an ultrasonic scanner that provides electrical signals for transmission of the ultrasound pulses towards the target region. The transmitted ultrasound pulses partially reflect back from the target region and cause vibrations in the transducer on receipt. The transducer converts the vibrations into signals that travel to the ultrasonic scanner where they are processed and transformed into a digital image of the target region, such as biological tissues.
Accordingly, one application of ultrasonography includes measuring tissue stiffness. Measurement of the shear or Young's modulus of tissue, or more simplistically, measuring the “stiffness” of the tissue is a useful tool for discriminating between healthy, diseased and injured biological tissues. Typically, at least a portion of a tissue may become stiffer than surrounding tissues indicating an onset or presence of a disease. By way of example, a relatively stiff region of a tissue may indicate cancer, tumor, fibrosis, steatosis or other such conditions.
Acoustic Radiation Force Impulse (ARFI) imaging is a radiation force based imaging technique that provides information about localized mechanical properties such as tissue stiffness. Particularly, ARFI imaging uses focused ultrasound to apply short duration localized radiation force impulses to a small volume of a tissue. These impulses, or pushing pulses, generate localized displacements of the tissue typically on the order of 1-10 μm. Conventional B-mode imaging pulses are then used to track the tissue displacements generated in response to the pushing pulses. By repeating ARFI sequences along multiple image lines, two-dimensional (2D) or three-dimensional (3D) images of the tissue displacements can be created. ARFI imaging, thus, is useful for observing lesions that are difficult to visualize with conventional sonography, but and are stiffer or softer than surrounding tissues.
Conventional ARFI imaging, however, suffers from time consuming data acquisition, high processing power requirements, loss of focus, low frame rates, and significant tissue and transducer heating. These issues arise in part because of the long round trip propagation time of the pulses along each scan line, the need for a large number of push locations and computations for imaging large areas of the tissue. Certain ARFI imaging techniques propose normalizing the tissue displacement over a depth or smaller apertures to mitigate beam focusing issues. Such techniques, however, typically result in lower beam intensity and poor signal-to-noise ratio outside a region of focus. Another technique uses multiple line acquisition to improve a frame rate while imaging by acquiring multiple scan lines in parallel for each transmitted pulse. Multiple line acquisition, however, results in reduced beam intensity and may also introduce artifacts that degrade image quality.
It is, thus, desirable to develop effective methods and systems for enhanced ARFI imaging performance. Particularly, there is a need for methods and systems, for example, that extend an effective depth range of ARFI imaging, improve the frame rate and spatial resolution while reducing the ultrasound radiation dosage.